Method for treating annular fissures in intervertebral discs

ABSTRACT

A percutaneous method of repairing a fissure in the annulus pulposus includes placing an energy source adjacent to the fissure and providing sufficient energy to the fissure to raise the temperature to at least about 45-70° C. and for a sufficient time to cause the collagen to weld. An intervertebral fissure also can be treated by placing a catheter with a lumen adjacent to the fissure and injecting sealant into the fissure via the catheter, thereby sealing the fissure. An intervertebral fissure additionally can be treated by providing a catheter having a distal end, a proximal end, a longitudinal axis, and an intradiscal section at the catheter&#39;s distal end on which there is at least one functional element. The next step is applying a force longitudinally to the proximal of the catheter which is sufficient to advance the intradiscal section through the nucleus pulposus and around an inner wall of an annulus fibrosus, but which force is insufficient to puncture the annulus fibrosus. Next the functional element is positioned at a selected location of the disc by advancing or retracting the catheter and optionally twisting the proximal end of the catheter. Then the functional unit treats the annular fissure. Optionally, there is an additional step of adding a substance to seal the fissure. An externally guidable intervertebral disc apparatus also is disclosed.

This application is a division of U.S. Application Nos. 08/881,527,08/881,692, 08/881,693, now U.S. Pat. No. 6,007,570, 08/881,694 filedJun. 24, 1997, which each claims priority to U.S. ProvisionalApplication Nos. 60/047,820, 60,047,841, 60/047,818, 60/047,848 filedMay 28, 1997, U.S. Provisional Application No. 60/045,941 filed May 8,1997, and U.S. Provisional Application Nos. 60/029,734, 60/029,735,60/029,600, 60/029,602 filed Oct. 23, 1996. Application Ser. Nos.08/881,525, 08/881,527, 08/881,692, 08/881,694, 60/029,600, 60/029,602,60/029,734, 60/029,735, 60/047,818 are each incoroporated herein byreference.

BACKGROUND

1. Field of the Invention

This invention relates to methods and apparatuses for modifyingintervertebral disc tissue and more particularly to the treatment ofannular fissures using percutaneous techniques to avoid major surgicalintervention.

2. Description of Related Art

Intervertebral disc abnormalities have a high incidence in thepopulation and may result in pain and discomfort if they impinge on orirritate nerves. Disc abnormalities may be the result of trauma,repetitive use, metabolic disorders and the aging process and includesuch disorders but are not limited to degenerative discs (i) localizedtears or fissures in the annulus fibrosus, (ii) localized discherniations with contained or escaped extrusions, and (iii) chronic,circumferential bulging disc.

Disc fissures occur rather easily after structural degeneration (a partof the aging process that may be accelerated by trauma) of fibrouscomponents of the annulus fibrosus. Sneezing, bending or just attritioncan tear these degenerated annulus fibers, creating a fissure. Thefissure may or may not be accompanied by extrusion of nucleus pulposusmaterial into or beyond the annulus fibrosus. The fissure itself may bethe sole morphological change, above and beyond generalized degenerativechanges in the connective tissue of the disc. Even if there is novisible extrusion, biochemicals within the disc may still irritatesurrounding structures. Disc fissures can be debilitatingly painful.Initial treatment is symptomatic, including bed rest, pain killers andmuscle relaxants. More recently spinal fusion with cages have beenperformed when conservative treatment did not relieve the pain. Thefissure may also be associated with a herniation of that portion of theannulus.

With a contained disc herniation, there are no free nucleus fragments inthe spinal canal. Nevertheless, even a contained disc herniation isproblematic because the outward protrusion can press on the spinalnerves or irritate other structures. In addition to nerve rootcompression, escaped nucleus pulposus contents may chemically irritateneural structures. Current treatment methods include reduction ofpressure on the annulus by removing some of the interior nucleuspulposus material by percutaneous nuclectomy. However, complicationsinclude disc space infection, nerve root injury, hematoma formation,instability of the adjacent vertebrae and collapse of the disc fromdecrease in height.

Another disc problem occurs when the disc bulges outwardcircumferentially in all directions and not just in one location. Overtime, the disc weakens and takes on a "roll" shape or circumferentialbulge. Mechanical stiffness of the joint is reduced and the joint maybecome unstable. One vertebra may settle on top of another. This problemcontinues as the body ages and accounts for shortened stature in oldage. With the increasing life expectancy of the population, suchdegenerative disc disease and impairment of nerve function are becomingmajor public health problems. As the disc "roll" extends beyond thenormal circumference, the disc height may be compromised, foramina withnerve roots are compressed. In addition, osteophytes may form on theouter surface of the disc roll and further encroach on the spinal canaland foramina through which nerves pass. The condition is called lumbarspondylosis.

It has been thought that such disc degeneration creates segmentalinstability which disturbs sensitive structures which in turn registerpain. Traditional, conservative methods of treatment include bed rest,pain medication, physical therapy or steroid injection. Upon failure ofconservative therapy, spinal pain (assumed to be due to instability) hasbeen treated by spinal fusion, with or without instrumentation, whichcauses the vertebrae above and below the disc to grow solidly togetherand form a single, solid piece of bone. The procedure is carried outwith or without discectomy. Other treatment include discectomy alone ordisc decompression with or without fusion. Nuclectomy can be performedby removing some of the nucleus to reduce pressure on the annulus.However, complications include disc space infection, nerve root injury,hematoma formation, and instability of adjacent vertebrae.

These interventions have been problematic in that alleviation of backpain is unpredictable even if surgery appears successful. In attempts toovercome these difficulties, new fixation devices have been introducedto the market, including but not limited to pedicle screws and interbodyfusion cages. Although pedicle screws provide a high fusion successrate, there is still no direct correlation between fusion success andpatient improvement in function and pain. Studies on fusion havedemonstrated success rate of between 50% and 67% for pain improvement,and a significant number of patients have more pain postoperatively.Therefore, different methods of helping patients with degenerative discproblems need to be explored.

FIGS. 1(a) and 1(b) illustrate a cross-sectional anatomical view of avertebra and associated disc and a lateral view of a portion of a lumbarand thoracic spine, respectively. Structures of a typical cervicalvertebra (superior aspect) are shown in FIG. 1(a): 104--lamina;106--spinal cord; 108--dorsal root of spinal nerve; 114--ventral root ofspinal nerve; 116--posterior longitudinal ligament; 118--intervertebraldisc; 120--nucleus pulposus; 122--annulus fibrosus; 124--anteriorlongitudinal ligament; 126--vertebral body; 128--pedicle; 130--vertebralartery; 132--vertebral veins; 134--superior articular facet;136--posterior lateral portion of the annulus; 138--posterior medialportion of the annulus; and 142--spinous process. In FIG. 1(a), one sideof the intervertebral disc 118 is not shown so that the anteriorvertebral body 126 can be seen. FIG. 1(b) is a lateral aspect of thelower portion of a typical spinal column showing the entire lumbarregion and part of the thoracic region and displaying the followingstructures: 118--intervertebral disc; 126--vertebral body; 142--spinousprocess; 170--inferior vertebral notch; 110--spinal nerve; 174--superiorarticular process; 176--lumbar curvature; and 180--sacrum.

The presence of the spinal cord and the posterior portion of thevertebral body, including the spinous process, and superior and inferiorarticular processes, prohibit introduction of a needle or trocar from adirectly posterior position. This is important because the posteriordisc wall is the site of symptomatic annulus tears and discprotrusions/extrusions that compress or irritate spinal nerves for mostdegenerative disc syndromes. The inferior articular process, along withthe pedicle and the lumbar spinal nerve, form a small "triangular"window (shown in black in FIG. 1(c)) through which introduction can beachieved from the posterior lateral approach. FIG. 1(d) looks down on aninstrument introduced by the posterior lateral approach. It is wellknown to those skilled in the art that percutaneous access to the discis achieved by placing an introducer into the disc from this posteriorlateral approach, but the triangular window does not allow much room tomaneuver. Once the introducer pierces the tough annulus fibrosus, theintroducer is fixed at two points along its length and has very littlefreedom of movement. Thus, this approach has allowed access only tosmall central and anterior portions of the nucleus pulposus. Currentmethods do not permit percutaneous access to the posterior half of thenucleus or to the posterior wall of the disc. Major and potentiallydangerous surgery is required to access these areas.

U.S. Pat. No. 5,433,739 (the "'739 patent") discloses placement of an RFelectrode in an interior region of the disc approximately at the centerof the disc. RF power is applied, and heat then putatively spreads outglobally throughout the disc. The '739 patent teaches the use of a rigidshaft which includes a sharpened distal end that penetrates through theannulus fibrosus and into the nucleus pulposus. In one embodiment theshaft has to be rigid enough to permit the distal end of the RFelectrode to pierce the annulus fibrosus, and the ability to maneuverits distal end within the nucleus pulposus is limited. In anotherembodiment, a somewhat more flexible shaft is disclosed. However,neither embodiment of the devices of the '739 patent permits access tothe posterior, posterior lateral and posterior medial region of thedisc, nor do they provide for focal delivery of therapy to a selectedlocal region within the disc or precise temperature control at theannulus. The '739 patent teaches the relief of pain by globally heatingthe disc. There is no disclosure of treating an annular tear or fissure.

U.S. Pat. No. 5,201,729 (the "'729 patent") discloses the use of anoptical fiber that is introduced into a nucleus pulposus. In the '729patent, the distal end of a stiff optical fiber shaft extends in alateral direction relative to a longitudinal axis of an introducer. Thisprevents delivery of coherent energy into the nucleus pulposus in thedirection of the longitudinal axis of the introducer. Due to theconstrained access from the posterior lateral approach, stiff shaft andlateral energy delivery, the device of the '729 patent is unable to gainclose proximity to selected portion(s) of the annulus (i.e., posterior,posterior medial and central posterior) requiring treatment or toprecisely control the temperature at the annulus. No use in treating anannular fissure is disclosed.

Accordingly, it is desirable to diagnose and treat disc abnormalities atlocations previously not accessible via percutaneous approaches andwithout substantial destruction to the disc. It would further bedesirable to be able to administer materials to a precise, selectedlocation within the disc, particularly to the location of the annularfissure. It would be further desirable to provide thermal energy intocollagen in the area of the fissure to strengthen the annulus andpossibly fuse collagen to the sides of the fissure, particularly at theposterior, posterior lateral and the posterior medial regions of theinner wall of the annulus fibrosus.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a minimallyinvasive method and apparatus for diagnosing and treating fissures ofdiscs at selected locations within the disc.

Another object of the invention is to provide an apparatus which isadvanceable and navigable at the inner wall of the annulus fibrosus toprovide localized heating at the site of the annular fissure.

Still a further object of the invention is to provide a device which hasa distal end that is inserted into the disc and accesses the posterior,posterior lateral and the posterior medial regions of the inner wall ofthe annulus fibrosus in order to repair or shrink an annular fissure atsuch a location.

These and other objects of the invention have been accomplished by thepresent invention which provides methods for manipulating a disc tissuewith a fissure or tear in an intervertebral disc, the disc having anucleus pulposus and an annulus fibrosus, the annulus having an innerwall of the annulus fibrosus. The method employs an externally guidableintervertebral disc apparatus, or catheter. The procedure is performedwith a catheter having a distal end, a proximal end, a longitudinalaxis, and an intradiscal section at the catheter's distal end on whichthere is at least one functional element. The catheter is advancedthrough the nucleus pulposus and around an inner wall of an annulusfibrosus by applying a force to the proximal end, but the applied forceis insufficient for the intradiscal section to puncture the annulusfibrosus. The next step is positioning the functional element at aselected location of the disc by advancing or retracting the catheterand optionally twisting the proximal end of the catheter. Then thefunctional unit treats the annular fissure.

A method of treating an intervertebral fissure comprises the steps ofplacing an energy source adjacent to the fissure and providingsufficient energy to the fissure to raise the temperature to at leastabout 45-70° C. and for a sufficient time to cause the collagen to weld.

Yet another method of treating an intervertebral fissure comprisesplacing a catheter with a lumen adjacent to the fissure and injectingsealant into the fissure via the catheter lumen to seal the fissure.

In addition to the method, there is provided an externally guidableintervertebral disc apparatus for diagnosis or manipulation of disctissue present at a selected location of an intervertebral disc, thedisc having a nucleus pulposus, an annulus fibrosus, and an inner wallof the annulus fibrosus, the nucleus pulposus having a diameter in adisc plane between opposing sections of the inner wall. The apparatuscomprises a catheter having a distal end, a proximal end, and alongitudinal axis, and an intradiscal section at the catheter's distalend, which is extendible into the disc, has sufficient rigidity to beadvanceable through the nucleus pulposus and around the inner wall ofthe annulus fibrosus under a force applied longitudinally to theproximal end, has sufficient flexibility in a direction of the discplane to be compliant with the inner wall, and has insufficientpenetration ability to be advanceable out through the annulus fibrosusunder the force; and a functional element located at the intradiscalsection for adding sufficient thermal energy at or near the fissure.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood by reference to the followingfigures that form part of the current specification, wherein:

FIG. 1(a) is a superior cross-sectional anatomical view of a cervicaldisc and vertebra.

FIG. 1(b) is a lateral anatomical view of a portion of a lumbar spine.

FIG. 1(c) is a posterior-lateral anatomical view of two lumbar vertebraeand illustration of the triangular working zone.

FIG. 1(d) is a superior cross-sectional view of the required posteriorlateral approach.

FIG. 2 is a second cross-sectional view of an intervertebral discillustrating a disc plane of the intervertebral disc and aninferior/superior plane.

FIG. 3(a) is a plan view of an introducer and an instrument of theinvention in which solid lines illustrate the position of the instrumentin the absence of bending forces and dotted lines indicate the positionthe distal portion of the instruments would assume under bending forcesapplied to the intradiscal section of the instrument.

FIG. 3(b) is an end view of the handle of the embodiment shown in FIG.3(a).

FIG. 4 is a cross-sectional view of an intervertebral disc with aportion of the intervertebral apparatus of the present inventioninserted in the intervertebral disc.

FIG. 5(a) is a cross-sectional view of the intervertebral segment of theembodiment of the invention shown in FIG. 3(a) taken along the line5(a)--5(a) of FIG. 3(a).

FIG. 5(b) is a cross-sectional view of the intervertebral segment of asecond embodiment of the present invention having a combinedwall/guiding mandrel.

FIG. 6 is a perspective view of an embodiment of an apparatus of thepresent invention with a resistive heating coil positioned around anexterior of an intradiscal section of the catheter.

FIG. 7 is a partial cross-sectional view of an embodiment an apparatusof the invention illustrating a sensor positioned in an interior of theintradiscal section of the catheter.

FIG. 8 is a partial cross-sectional view of an embodiment of theapparatus of the invention further including a sheath positioned aroundthe resistive heating coil.

FIG. 9 is a partial cross-sectional view of an embodiment of theapparatus of FIG. 6 with multiple resistive heating coils.

FIG. 10 is a plan view of an embodiment of the intradiscal section of acatheter of the invention with a helical structure.

FIG. 11 is a block diagram of an open or closed loop feedback systemthat couples one or more sensors to an energy source.

FIG. 12 is a block diagram of an embodiment illustrating an analogamplifier, analog multiplexer and microprocessor used with the feedbackcontrol system of FIG. 11.

The invention now being generally described, the same will be betterunderstood by reference to the following detailed description ofspecific embodiments and general features of the invention.

DETAILED DESCRIPTION

The present invention provides a method and apparatus for treatingintervertebral disc disorders, particularly fissures of the annulusfibrosus, which may or may not be accompanied with contained or escapedextrusions.

In general, an apparatus of the invention is in the form of anexternally guidable intervertebral disc apparatus for accessing andmanipulating disc tissue present at a selected location of anintervertebral disc having a nucleus pulposus and an annulus fibrosus,the annulus having an inner wall. Use of a temperature-controlled energydelivery element, combined with the navigational control of theinventive catheter, provides preferential, localized heating to treatthe fissure. For ease of reference to various manipulations anddistances described below, the nucleus pulposus can be considered ashaving a given diameter is a disc plane between opposing sections of theinner wall. This nucleus pulposus diameter measurement allows instrumentsizes (and parts of instruments) designed for one size disc to bereadily converted to sizes suitable for an instrument designed for adifferent size of disc.

The operational portion of the apparatus of the invention is brought toa location in or near the disc's fissure using techniques andapparatuses typical of percutaneous interventions. For convenience andto indicate that the apparatus of the invention can be used with anyinsertional apparatus that provides proximity to the disc, includingmany such insertional apparatuses known in the art, the term"introducer" is used to describe this aid to the method. An introducerhas an internal introducer lumen with a distal opening at a terminus ofthe introducer to allow insertion (and manipulation) of the operationalparts of the apparatus into (and in) the interior of a disc.

The operational part of the apparatus comprises an elongated elementreferred to as a catheter, various parts of which are located byreference to a distal end and a proximal end at opposite ends of itslongitudinal axis. The proximal end is the end closest to the externalenvironment surrounding the body being operated upon (which may still beinside the body in some embodiments if the catheter is attached to ahandle insertable into the introducer). The distal end of the catheteris intended to be located inside the disc under conditions of use. Thecatheter is not necessarily a traditional medical catheter (i.e., anelongate hollow tube for admission or removal of fluids from an internalbody cavity) but is a defined term for the purposes of thisspecification. "Catheter" has been selected as the operant word todescribe this part of the apparatus, as the inventive apparatus is along, flexible tube which transmits energy and/or material from alocation external to the body to a location internal to the disc beingaccessed upon, such as a collagen solution and heat to the annularfissure. Alternatively, material can be transported in the otherdirection to remove material from the disc, such as removing material byaspiration to decrease pressure which is keeping the fissure open andaggravating the symptoms due to the fissure.

The catheter is adapted to slidably advance through the introducerlumen, the catheter having an intradiscal section at the distal end ofthe catheter, the intradiscal section being extendible through thedistal opening at the terminus of the introducer into the disc. Althoughthe length of the intradiscal portion can vary with the intendedfunction as explained in detail below, a typical distance of extensionis at least one-half the diameter of the nucleus pulposus, preferably inthe range of one-half to one and one-half times the circumference of thenucleus.

In order that the functional elements of the catheter can be readilyguided to the desired location within a disc, the intradiscal portion ofthe catheter is manufactured with sufficient rigidity to avoidcollapsing upon itself while being advanced through the nucleus pulposusand navigated around the inner wall of the annulus fibrosus. Theintradiscal portion, however, has insufficient rigidity to puncture theannulus fibrosus under the same force used to advance the catheterthrough the nucleus pulposus and around the inner wall of the annulusfibrosus. Absolute penetration ability will vary with sharpness andstiffness of the tip of the catheter, but in all cases a catheter of thepresent invention will advance more readily through the nucleus pulposusthan through the annulus fibrosus.

In preferred embodiments, the intradiscal section of the catheterfurther has differential bending ability in two orthogonal directions atright angles to the longitudinal axis. This causes the catheter to bendalong a desired plane (instead of at random). Also when a torsional(twisting) force is applied to the proximal end of the catheter tore-orient the distal end of the catheter, controlled advancement of thecatheter in the desired plane is possible.

A further component of the catheter is a functional element located inthe intradiscal section for diagnosis or for adding energy and addingand/or removing material at the selected location of the disc where theannular tear is to be treated. The apparatus allows the functionalelement to be controllably guided by manipulation of the proximal end ofthe catheter into a selected location for localized treatment of theannular fissure.

The method of the invention, which involves manipulating disc tissue atthe annular fissure, is easily carried out with an apparatus of theinvention. An introducer is provided that is located in a patient's bodyso that its proximal end is external to the body and the distal openingof its lumen is internal to the body and (1) internal to the annulusfibrosus or (2) adjacent to an annular opening leading to the nucleuspulposus, such as an annular tear or trocar puncture that communicateswith the nucleus pulposus. The catheter is then slid into position inand through the introducer lumen so that the functional element in thecatheter is positioned at the selected location of the disc by advancingor retracting the catheter in the introducer lumen and optionallytwisting the proximal end of the catheter to precisely navigate thecatheter. By careful selection of the rigidity of the catheter and bymaking it sufficiently blunt to not penetrate the annulus fibrosus, andby careful selection of the flexibility in one plane versus theorthogonal plane, the distal portion of the catheter will curve alongthe inner wall of the annulus fibrosus as it is navigated and isselectively guided to an annular tear at selected location(s) in thedisc. Energy is applied and/or material is added or removed at theselected location of the disc via the functional element.

Each of the elements of the apparatus and method will now be describedin more detail. However, a brief description of disc anatomy is providedfirst, as sizes and orientation of structural elements of the apparatusand operations of the method can be better understood in some cases byreference to disc anatomy.

The annulus fibrosus is comprised primarily of tough fibrous material,while the nucleus pulposus is comprised primarily of an amorphouscolloidal gel. There is a transition zone between the annulus fibrosusand the nucleus pulposus made of both fibrous-like material andamorphous colloidal gel. The border between the annulus fibrosus and thenucleus pulposus becomes more difficult to distinguish as a patientages, due to degenerative changes. This process may begin as early as 30years of age. For purposes of this specification, the inner wall of theannulus fibrosus can include the young wall comprised primarily offibrous material as well as the transition zone which includes bothfibrous material and amorphous colloidal gels (hereafter collectivelyreferred to as the "inner wall of the annulus fibrosus"). Functionally,that location at which there is an increase in resistance to catheterpenetration and which is sufficient to cause bending of the distalportion of the catheter into a radius less than that of the internalwall of the annulus fibrosus is considered to be the "inner wall of theannulus fibrosus".

As with any medical instrument and method, not all patients can betreated, especially when their disease or injury is too severe. There isa medical gradation of degenerative disc disease (stages 1-5). See, forexample, Adams et al., "The Stages of Disc Degeneration as Revealed byDiscograms," J. Bone and Joint Surgery, 68, 36-41 (1986). As thesegrades are commonly understood, the methods of instrument navigationdescribed herein would probably not be able to distinguish between thenucleus and the annulus in degenerative disease of grade 5. In any case,most treatment is expected to be performed in discs in stages 3 and 4,as stages 1 and 2 are asymptomatic in most patients, and stage 5mayrequire disc removal and fusion.

Some of the following discussion refers to motion of the catheter insidethe disc by use of the terms "disc plane" "oblique plane" and"cephalo-caudal plane." These specific terms refer to orientations ofthe catheter within the intervertebral disc. Referring now to FIG. 2(which shows a vertical cross-section of a disc), a disc plane 30 of theintervertebral disc is generally a plane of some thickness 27 within thenucleus pulposus 120 orthogonal to the axis formed by the spinal column(i.e., such a disc plane is substantially horizontal in a standinghuman, corresponding to the "flat" surface of a vertebra). A obliqueplane 31 extends along any tilted orientation relative to axial plane30; however, when the plane is tilted 90°, such a plane would besubstantially vertical in a standing human and is referred to as acephalo-caudal plane. Reference is made to such planes to describecatheter movements with respect to the disc plane. In variousembodiments, disc plane 30 has a thickness no greater than the thicknessof the intervertebral disc, preferably a thickness no greater than 75%of a thickness of the intervertebral disc, and more preferably athickness no greater than 50% of a thickness of the intervertebral disc.Movement of the intradiscal portion 16 of catheter 14 is confined withina disc plane by the physical and mechanical properties of theintradiscal portion 16 during advancement of the catheter when thebending plane of the catheter is aligned with the disc plane, until someadditional force is applied to the catheter by the physician. A twistingforce (which can be applied mechanically, electrically, or by any othermeans) acting on the proximal end of the catheter changes the forcesacting on the distal end of the catheter so that the plane of thecatheter bend can be angled relative to the disc plane as the catheteris advanced. Thus, the physician can cause the distal end of thecatheter to move up or down, depending on the direction of the twist.

Turning now to the introducer, a detailed description of an entireapparatus should not be necessary for those skilled in the art ofpercutaneous procedures and the design of instruments intended for suchuse. The method of the invention can also be carried out with endoscopicinstruments, and an endoscopic apparatus having structural parts thatmeet the descriptions set forth in this specification would also be anapparatus of the invention.

In general, a device of the invention can be prepared in a number ofdifferent forms and can consist (for example) of a single instrumentwith multiple internal parts or a series of instruments that can bereplaceably and sequentially inserted into a hollow fixed instrument(such as a needle) that guides the operational instruments to a selectedlocation in or adjacent to an annular fissure. Because prior patents donot fully agree on how to describe parts of percutaneous instruments,terminology with the widest common usage will be used.

The introducer, in its simplest form, can consist of a hollowneedle-like device (optionally fitted with an internal removableobturator or trocar to prevent clogging during initial insertion) or acombination of a simple exterior cannula that fits around a trocar. Theresult is essentially the same: placement of a hollow tube (the needleor exterior cannula after removal of the obturator or trocar,respectively) through skin and tissue to provide access into the annulusfibrosus. The hollow introducer acts as a guide for introducinginstrumentation. More complex variations exist in percutaneousinstruments designed for other parts of the body and can be applied todesign of instruments intended for disc operations. Examples of suchobturators are well known in the art. A particularly preferredintroducer is a 17- or 18-gauge, thin-wall needle with a matchedobturator, which after insertion is replaced with a catheter of thepresent invention.

Referring now to the figures, FIGS. 3(a) and 3(b) illustrate oneembodiment of a catheter 14 of the invention as it would appear insertedinto an introducer 12. The apparatus shown is not to scale, as anexemplary apparatus (as will be clear from the device dimensions below)would be relatively longer and thinner; the proportions used in FIG.3(a) were selected for easier viewing by the reader. The distal portionof an intervertebral apparatus operates inside an introducer 12 havingan internal introducer lumen 13. A flexible, movable catheter 14 is atleast partially positionable in the introducer lumen 13. Catheter 14includes a distal end section 16 referred to as the intradiscal section,which is designed to be the portion of the catheter that will be pushedout of the introducer lumen and into the nucleus pulposus, wheremovement of the catheter will be controlled to bring operationalportions of the catheter into the selected location(s) with regard tothe annular tear. In FIG. 3(a), dashed lines are used to illustratebending of the intradiscal portion of the catheter as it might appearunder use, as discussed in detail later in the specification. FIG. 3(b)shows an end view of handle 11 at the proximal end of the catheter, withthe handle 11 having an oval shape to indicate the plane of bending,also discussed in detail later in the specification. Other sections andproperties of catheter 14 are described later.

For one embodiment suitable for intervertebral discs, the outer diameterof catheter 14 is in the range of 0.2 to 5 mm, the total length ofcatheter 14 (including the portion inside the introducer) is in therange of 10 to 60 cm, and the length of introducer 12 is in the range of5 to 50 cm. For one preferred embodiment, the catheter has a diameter of1 mm, an overall length of 30 cm, and an introduced length of 15 cm (forthe intradiscal section). With an instrument of this size, a physiciancan insert the catheter for a distance sufficient to reach selectedlocation(s) in the nucleus of a human intervertebral disc.

FIG. 4 illustrates the anatomy of an intervertebral disc and shows anapparatus of the invention inserted into a disc. Structures of the discare identified and described by these anatomical designations: theposterior lateral inner annulus 136, posterior medial inner annulus 138,annulus fibrosus 122/nucleus pulposus 120 interface, the annulus/duralinterface 146, annulus/posterior longitudinal ligament interface 148,anterior lateral inner annulus 150, and the anterior medial innerannulus 152.

Referring again to FIG. 4, the mechanical characteristics of intradiscalsection 16 of catheter 14 are selected to have (1) sufficient columnstrength along the longitudinal axis of the catheter to avoid collapseof the catheter and (2) different flexural strengths along the two axesorthogonal to the longitudinal axis to allow controlled bending of thecatheter. These parameters make the catheter conformable and guidablealong inner wall 22 of an annulus fibrosus 122 to reach selectedlocation(s), such as the posterior medial annulus 138.

Specific mechanical characteristics of particular designs will bedescribed later in the examples that follow. Generally, however, thenecessary design features can be selected (in an interrelated fashion)by first providing the intradiscal section of the catheter withsufficient column strength to be advanceable through normal humannucleus pulposus and around the inner wall of the annulus fibrosuswithout collapse. Here "collapse" refers to bending sufficient toinhibit further advancement at the tip. Advancement of the tip isrestricted by 1) sliding through the normal gelatinous nucleus pulposus,2) contacting denser clumps of nucleus pulposus, and 3) curving andadvancing along the inner wall of the annulus. Column strength can beincreased in many ways known in the art, including but not limited toselecting materials (e.g., metal alloy or plastic) with a highresistance to bending from which to form the catheter, forming thestructure of the catheter with elements that add stiffening (such asbracing), and increasing the thickness of the structural materials.Column strength can be decreased to favor bending by selecting theopposite characteristics (e.g., soft alloys, hinging, and thinstructural elements).

When the catheter collapses, the physician feels an abrupt decrease inresistance. At that time, the catheter forms one or more loops or kinksbetween the tip of the introducer and the distal tip of the catheter.

Particularly preferred for annular tears at the posterior of theannulus, the tip 28 of intradiscal section 16 is biased or otherwisemanufactured so that it forms a pre-bent segment prior to contact withthe annulus fibrosus as shown in FIG. 3(a). The bent tip will cause theintradiscal section to tend to continue to bend the catheter in the samedirection as the catheter is advanced. This enhanced curving of apre-bent catheter is preferred for a catheter that is designed to reacha posterior region of the nucleus pulposus; however, such a cathetermust have sufficient column strength to prevent the catheter fromcollapsing back on itself.

The intradiscal section not only must allow bending around therelatively stronger annulus fibrosus in one direction, but also resistbending in the orthogonal direction to the plane in which bending isdesigned to occur. By twisting the proximal end of a catheter and thuscontrolling the orientation of the plane of bending while concurrentlycontrolling the advancement of the catheter through the nucleus, aphysician can navigate the catheter and its instrumentation within thedisc.

The bending stiffness of the intradiscal section as measured in Taberstiffness units (using a length of the inventive catheter as the teststrip rather than the standard dimension, homogeneous-material teststrip) should be in the range of 2-400 units (in a 0-10,000 unit range)in the desired bending plane, preferably 3-150 units. In preferredembodiments, stiffness is in the range of 4-30 units in the desiredbending plane. In all cases, the bending stiffness preferably is 2-20times higher for bending in the orthogonal direction.

The column or compressive strength of the intradiscal section (forcerequired to buckle a segment whose length is 25 or more times itsdiameter) is in the range of 0.05 to 4 kg, preferably 0.05 to 2 kg. Inthe most preferred embodiments, it is in the range of 0.1 to 1 kg. Inthe proximal shaft section (i.e., the part of the catheter proximal tothe intradiscal section), this strength is in the range of 0.1 to 25 kg,preferably 0.2 to 7 kg. In the most preferred embodiments, it is in therange of 0.7 to 4 kg.

Returning now to FIG. 4, intradiscal section 16 is guidable and canreach the posterior, the posterior lateral, and the posterior medialregions of the posterior wall of the annulus fibrosus, as well as otherselected section(s) on or adjacent to inner wall 22. In order to movethe functional section of the catheter into a desired nucleus location,intradiscal section 16 is first positioned in the nucleus pulposus 120by means of the introducer.

In most uses, introducer 12 pierces annulus fibrosus 122 and is advancedthrough the wall of the annulus fibrosus into the nucleus pulposus. Insuch embodiments, introducer 12 is then extended a desired distance intonucleus pulposus 120. Catheter 14 is advanced through a distal end ofintroducer 12 into nucleus pulposus 120. Advancement of the catheter 14,combined with increased resistance to advancement at the annulusfibrosus, causes the tip of the intradiscal section to bend relative tothe longitudinal axis of introducer 12 when the intradiscal sectioncontacts the inner wall of the annulus fibrosus 122. Catheter 14 isnavigated along inner wall 22 of annulus fibrosus 122 to selectedsite(s) of inner wall 22 or within nucleus pulposus 120. For example,intradiscal section 16 can be positioned in or adjacent to a fissure ortear 44 of annulus fibrosus 122.

The distal portion 28 of intradiscal section 16 is designed to beincapable of piercing the annulus fibrosus 122. The inability of distalportion 28 to pierce the annulus can be the result of either shape ofthe tip 29 or flexibility of distal portion 28, or both. The tip 29 isconsidered sufficiently blunt when it does not penetrate the annulusfibrosus but is deflected back into the nucleus pulposus or to the sidearound the inner wall of the annulus when the tip 29 is advanced. Thetip can be made with a freely rotating ball. This embodiment providesnot only a blunt surface but also a rolling contact to facilitatenavigation.

Many percutaneous and endoscopic instruments designed for other purposescan be adapted for use in this invention. This permits other functionsat the desired location after the catheter is advanced to that position.For example, cutting edges and sharp points can be present in the distalportion 28 if they can be temporarily masked by a covering element.However, such devices must be sufficiently flexible and thin to meet thedesign characteristics described in this specification.

In another embodiment an introducer 12 pierces the skin and reaches anexterior of annulus fibrosus 122. A rigid and sharp trocar is thenadvanced through introducer 12, to pierce annulus fibrosus 122 and enterthe disc. The trocar is then removed, and catheter 14 is advancedthrough a distal end of introducer 12, following the path created by thetrocar in annulus fibrosus 122 beyond the end of the introducer. In suchcases, the introducer is outside the annulus fibrosus 122 and only thecatheter with its guidable distal portion 16 is present inside the disc.The physician can manipulate the proximal portion 15 of the catheter tomove the distal portion of the catheter to a selected location fortreating a fissure of the annulus fibrosus 122.

Catheter 14 is not always pre-bent as shown in FIG. 3(a), but optionallycan include a biased distal portion 28 if desired. "Pre-bent" or"biased" means that a portion of the catheter (or other structuralelement under discussion) is made of a spring-like material that is bentin the absence of external stress but which, under selected stressconditions (for example, while the catheter is inside the introducer),is linear. Such a biased distal portion can be manufactured from eitherspring metal or superelastic memory material (such as Tinel®nickel-titanium alloy, Raychem Corp., Menlo Park Calif.). The introducer(at least in the case of a spring-like material for forming thecatheter) is sufficiently strong to resist the bending action of thebent tip and maintain the biased distal portion in alignment as itpasses through the introducer. Compared to unbiased catheters, acatheter with a biased distal portion 28 encourages advancement ofintradiscal section 16 substantially in the direction of the bendrelative to other lateral directions as shown by the bent location ofintradiscal section 16 indicated by dashed lines in FIG. 3(a). Biasingthe catheter tip also further decreases likelihood that the tip 29 willbe forced through the annulus fibrosus under the pressure used toadvance the catheter.

In addition to biasing a catheter tip prior to insertion into anintroducer, a catheter tip can be provided that is deflected bymechanical means, such as a wire attached to one side of the tip thatdeflects the tip in the desired direction upon application of force tothe proximal end of the deflection wire. Any device in which bending ofthe tip of a catheter of the invention is controlled by the physician is"actively steerable." In addition to a tip that is actively steerable byaction of a wire, other methods of providing a bending force at the tipcan be used, such as hydraulic pressure and electromagnetic force (suchas heating a shaped memory alloy to cause it to contract). Any of anumber of techniques can be used to provide selective bending of thecatheter in one lateral direction.

Referring now to FIG. 5(a), a guiding mandrel 32 can be included both toadd rigidity to the catheter and to inhibit movement of catheter 14 inthe inferior and superior directions while positioned and aligned in thedisc plane of a nucleus pulposus 120. This aids the functions ofpreventing undesired contact with a vertebra and facilitatingnavigation. The mandrel can be flattened to encourage bending in a plane(the "plane of the bend") orthogonal to the "flat" side of the mandrel."Flat" here is a relative term, as the mandrel can have a D-shapedcross-section, or even an oval or other cross-sectional shape without aplanar face on any part of the structure. Regardless of the exactconfiguration, bending will preferentially occur in the plane formed bythe principal longitudinal axis of the mandrel and a line connecting theopposite sides of the shortest cross-sectional dimension of the mandrel(the "thin" dimension). To provide sufficient resistance to the catheterbending out of the desired plane while encouraging bending in thedesired plane, the minimum ratio is 1.25:1 ("thickest" to "thinnest"cross-sectional dimensions along at least a portion of the intradiscalsection). The maximum ratio is 20:1, with the preferred ratio beingbetween 1.5:1 and 16:3, more preferably between 2:1 and 3.5:1. Theseratios are for a solid mandrel and apply to any material, as deflectionunder stress for uniform solids is inversely proportional to thethickness of the solid in the direction (dimension) in which bending istaking place. For other types of mandrels (e.g., hollow or non-uniformmaterials), selection of dimensions and/or materials that provide thesame relative bending motions under stress are preferred.

A catheter of the present invention is designed with sufficienttorsional strength (resistance to twisting) to prevent undesireddirectional movement of the catheter. Mandrels formed from materialshaving tensile strengths in the range set forth in the examples of thisspecification provide a portion of the desired torsional strength. Othermaterials can be substituted so long as they provide the operationalfunctions described in the examples and desired operating parameters.

While the mandrel can provide a significant portion of the columnstrength, selective flexibility, and torsional strength of a catheter,other structural elements of the catheter also contribute to thesecharacteristics. Accordingly, it must be kept in mind that it is thecharacteristics of the overall catheter that determine suitability of aparticular catheter for use in the methods of the invention. Forexample, a mandrel that does not have sufficient torsional strength whenacting alone can be combined with another element, such as anti-twistingouter sheath 40 or inserting/advancing a second mandrel, to provide acatheter of the invention. Similarly, components inside the catheter,such as a heating element or potting compound, can be used to strengthenthe catheter or provide directional flexibility at the locations ofthese elements along the catheter.

It is not necessary that the guiding mandrel 32 be flattened along itsentire length. Different mandrels can be designed for different sizeddiscs, both because of variations in disc sizes from individual toindividual and because of variations in size from disc to disc in onepatient. The bendable portion of the mandrel is preferably sufficient toallow intradiscal portion 16 of the catheter to navigate at leastpartially around the circumference of the inner wall of the annulusfibrosus (so that the operational functions of the catheter can becarried out at desired location(s) along the inner wall of the annulusfibrosus). Shorter bendable sections are acceptable for specializedinstruments. In most cases, a flattened distal portion of the mandrel ofat least 10 mm, preferably 25 mm, is satisfactory. The flattened portioncan extend as much as the entire length of the mandrel, with someembodiments being flattened for less than 15 cm, in other cases for lessthan 10 cm, of the distal end of the guide mandrel.

In preferred embodiments the guide mandrel or other differential bendingcontrol element is maintained in a readily determinable orientation by acontrol element located at the proximal end of the catheter. Theorientation of the direction of bending and its amount can be readilyobserved and controlled by the physician. One possible control elementis simply a portion of the mandrel that extends out of the proximal endof the introducer and can be grasped by the physician, with a shapebeing provided that enables the physician to determine the orientationof the distal portion by orientation of the portion in the hand. Forexample, a flattened shape can be provided that mimics the shape at thedistal end (optionally made larger to allow better control in the glovedhand of the physician, as in the handle 11 of FIG. 3(b)). More complexproximal control elements capable of grasping the proximal end of themandrel or other bending control element can be used if desired,including but not limited to electronic, mechanical, and hydrauliccontrols for actuation by the physician.

The guide mandrel can also provide the function of differentialflexibility by varying the thickness in one or more dimensions (forexample, the "thin" dimension, the "thick" dimension, or both) along thelength of the mandrel. A guide mandrel that tapers (becomes graduallythinner) toward the distal tip of the mandrel will be more flexible andeasier to bend at the tip than it is at other locations along themandrel. A guide mandrel that has a thicker or more rounded tip thanmore proximal portions of the mandrel will resist bending at the tip butaid bending at more proximal locations. Thickening (or thinning) canalso occur in other locations along the mandrel. Control of thedirection of bending can be accomplished by making the mandrel moreround, i.e., closer to having 1:1 diameter ratios; flatter in differentsections of the mandrel; or by varying the absolute dimensions(increasing or decreasing the diameter). Such control over flexibilityallows instruments to be designed that minimize bending in some desiredlocations (such as the location of connector of an electrical element toavoid disruption of the connection) while encouraging bending in otherlocations (e.g., between sensitive functional elements). In this manner,a catheter that is uniformly flexible along its entire length, isvariably flexibility along its entire length, or has alternating moreflexible and less flexible segment(s), is readily obtained simply bymanufacturing the guide mandrel with appropriate thickness at differentdistances and indifferent orientations along the length of the mandrel.Such a catheter will have two or more different radii of curvature indifferent segments of the catheter under the same bending force.

In some preferred embodiments, the most distal 3 to 40 mm of a guidemandrel is thinner relative to central portions of the intradiscalsection to provide greater flexibility, with the proximal 10 to 40 mm ofthe intradiscal section being thicker and less flexible to add columnstrength and facilitate navigation.

The actual dimensions of the guide mandrel will vary with the stiffnessand tensile strength of the material used to form the mandrel. In mostcases the mandrel will be formed from a metal (elemental or an alloy) orplastic that will be selected so that the resulting catheter will havecharacteristics of stiffness and bending that fall within the statedlimits. Additional examples of ways to vary the stiffness and tensilestrength include transverse breaks ion a material, advance of thematerial so that it "doubles up," additional layers of the same ordifferent material, tensioning or relaxing tension on the catheter, andapplying electricity to a memory metal.

As illustrated in FIG. 5(b), in some embodiments of an apparatus of theinvention, guiding mandrel is combined with at least a portion of thecatheter 14 to form a structure which provides the functions of both, awall/mandrel 41. In this figure, the wall/mandrel 41 of catheter 14 canbe varied in dimensions as described in the previous section of thisspecification directed to a separate mandrel, with the same resultingchanges in function. For example, changing the thickness of thewall/mandrel 41 that functions as the mandrel portion changes theflexibility and preferred direction of bending of the catheter. In manycases, the wall/mandrel 41 will be thinner than other portions of thecatheter wall 33 so that wall/mandrel 41 controls bending.Alternatively, wall/mandrel 41 can be formed of a different materialthan the other portions 33 of the catheter walls (i.e., one with a lowertensile and/or flexural strength) in order to facilitate bending.

Returning now to FIG. 5(a), the guiding mandrel 32 is generally locatedin the interior of catheter 14, where it shares space with otherfunctional elements of the catheter. For example and as shown in FIG.5(a), thermal energy delivery device lumen 34 can receive any of avariety of different couplings from an energy source 20 to a thermalenergy delivery device (functional element) further along the catheter,including but not limited to a wire or other connector between thermalenergy elements. Alternatively or concurrently, hollow lumen(s) 36 fordelivery or removal of a fluid or solid connectors for application of aforce to a mechanical element can be present, so no limitation should beplaced on the types of energy, force, or material transporting elementspresent in the catheter. These are merely some of the possiblealternative functional elements that can be included in the intradiscalportion of that catheter. Accordingly, a general description will now begiven of some of the possible functional elements.

Since the purpose of the inventive catheter is to repair tears orfissures in a disc by operation of the instrument at the tear locationadjacent to or inside the disc, a functional element is provided in oron the catheter to carry out that purpose.

Non-limiting examples of functional elements include any element capableof aiding diagnosis, delivering energy, or delivering or removing amaterial form a location adjacent the element's location in thecatheter, such as an opening in the catheter for delivery of a fluid(e.g., dissolved collagen to seal the fissure) or for suction, a thermalenergy delivery device (heat source), a mechanical grasping tool forremoving or depositing a solid, a cutting tool (which includes allsimilar operations, such as puncturing), a sensor for measurement of afunction (such as electrical resistance, temperature, or mechanicalstrength), or a functional element having a combination of thesefunctions.

The functional element can be at varied locations in the intradiscalportion of the catheter, depending on its intended use. Multiplefunctional elements can be present, such as multiple functional elementsof different types (e.g., a heat source and a temperature sensor) ormultiple functional elements of the same type (e.g., multiple heatsources spaced along the intradiscal portion).

One of the possible functional elements present on intradiscal section16 is a thermal energy delivery device 18. A variety of different typesof thermal energy can be delivered including but not limited toresistive heat, radiofrequency (RF), coherent and incoherent light,microwave, ultrasound and liquid thermal jet energies. In oneembodiment, thermal energy delivery device 18 is positioned proximal tothe distal portion of intradiscal section 16 so that there is nosubstantial delivery of energy at the distal portion, which can thenperform other functions without being constrained by being required toprovide energy (or resist the resulting heat).

Some embodiments have an interior infusion lumen 36. Infusion lumen 36is configured to transport a variety of different mediums including butnot limited to electrolytic solutions (such as normal saline), contrastmedia (such as Conray meglumine iothalamate), pharmaceutical agents,disinfectants, filling or binding materials such as collagens orcements, chemonucleolytic agents and the like, from a reservoir exteriorto the patient to a desired location within the interior of a disc(i.e., the fissure). Further, infusion lumen 36 can be used as anaspiration lumen to remove nucleus material or excess liquid or gas(naturally present, present as the result of a liquefying operation, orpresent because of prior introduction) from the interior of a disc. Whenused to transport a fluid for irrigation of the location within thedisc, the infusion lumen is sometimes referred to as an irrigationlumen. Infusion lumen 36 can be coupled to medium reservoir 21 throughthe catheter (see FIG. 3(a).

Included in the particular embodiment shown in this figure is one ormore sensor lumens 42. An example is a wire connecting a thermal sensorat a distal portion of the catheter to control elements attached to aconnector in the proximal handle 11 of the catheter.

Also included in the embodiment shown in FIG. 5(a) is an optional energydirecting device 43 including but not limited to a thermal reflector, anoptical reflector, thermal insulator, or electrical insulator. Energydirecting device 43 is configured to limit thermal and/orelectromagnetic energy delivery to a selected site of the disc and toleave other sections of the disc substantially unaffected. Energydirecting device 43 can be positioned on an exterior surface of catheterintradiscal section 16 and/or catheter 14 as well as in an internalportion of the catheter intradiscal section 16 and/or catheter 14. Forexample, the energy can be directed to the walls of the fissure tocauterize granulation tissue and to shrink the collagen component of theannulus, while the nucleus is shielded from excess heat.

In one embodiment, catheter intradiscal section 16 and/or distal portion28 are positionable to selected site(s) around and/or adjacent to innerwall 22 of annulus fibrosus 122 for the delivery of therapeutic and/ordiagnostic agents including but not limited to, electromagnetic energy,electrolytic solutions, contrast media, pharmaceutical agents,disinfectants, collagens, cements, chemonucleolytic agents and thermalenergy. Intradiscal section 16 is navigational and can reach theposterior, the posterior lateral, the posterior medial, anteriorlateral, and anterior medial regions of the annulus fibrosus, as well asselected section(s) on or adjacent to inner wall 22.

In a preferred embodiment, intradiscal section 16 is positioned adjacentto the entire posterior wall of the disc. Sufficient thermal energy canthen be delivered, for example, to selectively heat he posterior annulusto cauterize granulation tissue and shrink the collagen component of thewall around and adjacent to fissure 44 without undue damage to otherportions of the intervertebral disc, particularly the nucleus. Theseactions help close the fissure in the annulus.

In the preferred embodiment of FIG. 5(a), markings 38 are visible on theportion of the catheter that is located during normal operation outsidethe body being acted upon, particularly for embodiments in which theproximal end of the catheter is designed to be directly manipulated bthe hand of the physician. Advancement of the catheter into theintroducer will advance the markings into the introducer, therebyshowing how far the catheter has been advanced into the nucleus. Such avisible marking 38 can be positioned on an exterior surface of thecatheter or can be present on an interior surface and visible through atransparent outer covering or sheath. Preferred are visible markingsevery centimeter to aid the physician in estimating the catheter tipadvancement.

If desired, visible markings can also be used to show twisting motionsof the catheter to indicate the orientation of the bending plane of thedistal portion of the catheter. It is preferred, however, to indicatethe distal bending plane by the shape and feel of the proximal end ofthe catheter assembly. The catheter can be attached to or shaped into ahandle 11 that fits the hand of the physician and also indicates theorientation of the distal bending plane. Both the markings and thehandle shape thus act as control elements to provide control over theorientation of the bending plane; other control elements, such asplungers or buttons that act on mechanical, hydrostatic, electrical, orother types of controls, can be present in more complex embodiments ofthe invention.

Additionally, a radiographically opaque marking device can be includedin the distal portion of the catheter (such as in the tip or at spacedlocations throughout the intradiscal portion) so that advancement andpositioning of the intradiscal section can be directly observed byradiographic imaging. Such radiographically opaque markings arepreferred when the intradiscal section is not clearly visible byradiographic imaging, such as when the majority of the catheter is madeof plastic instead of metal. A radiographically opaque marking can beany of the known (or newly discovered) materials or devices withsignificant opacity. Examples include but are not limited to a steelmandrel sufficiently thick to be visible on fluoroscopy, atantalum/polyurethane tip, a gold-plated tip, bands of platinum,stainless steel or gold, soldered spots of gold and polymeric materialswith radiographically opaque filler such as barium sulfate. A resistiveheating element or an RF electrode(s) may provide sufficientratio-opacity in some embodiments to serve as a marking device.

A sheath 40 can optionally be positioned around catheter 14. Sheath 40provides a flexible surface that is smooth and provides for easyintroduction into a selected area within the disc. Sheath 40 can be madeof a variety of different materials including but not limited topolyester, rayon, polyimide, polyurethane, polyethylene, polyamide andsilicone. When visible markings are present to indicate the advancementof the catheter, either the sheath carries the markings, or the sheathis clear to reveal markings underneath.

In one preferred embodiment, thermal energy delivery device 18 is aresistive heating device. As illustrated in FIG. 6, a heating coil 46 ispositioned around an exterior of catheter 14. The heating element 46need not be in the shape of a coil. For instance, the heating elementcan be in the form of a thin flexible circuit which is mountable on orin substantially one side of the intradiscal portion of the catheter.Heating element 46 is powered by a direct current source 20 (and lesspreferably a source of alternating current). Heating element is made ofa material that acts as a resistor. Suitable materials include but arenot limited to stainless steel, nickel/chrome alloys, platinum, and thelike.

Preferably, the heating element is inside the intradiscal section ofcatheter 14 (FIG. 8). The resistive material is electrically insulatedand substantially no current escapes into the body. With increasinglevels of current, element 46 hats to greater temperature levels.Additionally, a circuit can be completed substantially entirely atintradiscal section 16 and a controllable delivery of thermal energy isachieved. In one embodiment, 2 watts pass through heating element 46 toproduce a temperature of about 55° C. in a selected target such asfissure 44, 3 watts produces 65° C., 4 watts produces 75° C., and so on.

In another embodiment, thermal energy delivery device 18 is areadiofrequency electrode, such as a band or coil. As illustrated inFIG. 6, RF electrode 46 is positioned on an exterior of catheter 14. RFelectrode 46 is powered by an RF generator. The electrode is made ofsuitable materials including but not limited to stainless steel orplatinum. The RF electrode is located on intradiscal section of catheter14. Increasing levels of current conducted into disc tissue heat thattissue to greater temperature levels. A circuit can be completedsubstantially entirely at intradiscal section 16 (bipolar device) or byuse of a second electrode attached to another portion of he patient'sbody (monopolar device). In either case, a controllable delivery of RFenergy is achieved.

In another embodiment sufficient energy is delivered to theintervertebral disc to heat and shrink the collagen component of theannulus but not ablate tissue adjacent to catheter 14.

With a resistive heating device, the amount of thermal energy deliveredto the tissue is a function of (i) the amount of current passing throughheating element 46, (ii) the length, shape, and/or size of heatingelement 46, (iii) the resistive properties of heating element 46, (iv)the gauge of heating element 46, and (v) the use of cooling fluid tocontrol temperature. All of these factors can be varied individually orin combination to provide the desired level of heat. Power supply 20associated with heating element 46 may be battery based. Catheter 14 canbe sterilized and may be disposable.

Referring now to FIG. 7, a thermal sensor 48 may be positioned in aninterior location of catheter 14. In another embodiment, thermal sensor48 is positioned on an exterior surface of catheter 14. A thermal sensorcan be used to control the delivery of energy to thermal energy deliverydevice 18. A potting material can be used to fix the position of thermalsensor 48 and provide a larger area from which to average the measuredtemperature. Thermal sensor 48 is of conventional design, including butnot limited to a thermistor; T type thermocouple with a copperconstantan junction; J type E type, and K type thermocouples; fiberoptics; resistive wires; IR detectors; and the like. Optionally, theremay be a lumen 42 for he thermal sensor connection.

As illustrated in FIG. 8, sheath 40 may be used to cover resistiveheating element 46. A plurality of resistive heating elements 46 can beused (FIG. 9) in a catheter of the invention.

Referring now to the embodiment shown in FIG. 10, thermal energydelivery device 18 comprises one or more resistive heating elements 46coupled to a resistive heating energy source. Resistive heating elements46 are positioned along intradiscal section 16 at locations where theycontrollably deliver thermal energy to selected structures, includinggranulation tissue in a fissure 44 and the annulus surrounding thefissure. Resistive heating elements 46 can be segmented and multiplexedso that only certain resistive heating elements, or combinations ofresistive heating elements are activated at any one particular time.Thermal sensor 48 can be positioned between resistive heating elements46 and/or at an exterior or interior locations of catheter 14. In theembodiment illustrated in FIG. 10, catheter 14 can be prepared with awound helical structural element 49 to increase flexibility and minimizekinking. However, other structures and geometries are suitable forcatheter 14, including but not limited to a substantially smooth surface(and specifically including the devices using an internal guide mandrelas previously described). For example, a sheath can be provided over theheating element, and the guiding mandrel inside the coil can beencapsulated in silicone potting material. The tubing flexibility andthe silicone potting material prevent kinking. Additionally, sheath 40an be positioned around catheter 14 and also around resistive heatingelements 46 to afford a substantially smooth surface. Resistive heatingelements 46 can be at least partially covered by a thermally insulatingmaterial, for example, along one side of the catheter, to selectivelyheat disc tissue on the opposite side.

Referring now to FIGS. 11 and 12, an open or closed loop feedback system52 couples sensors 48 to energy source 20. As illustrated in FIG. 10,thermal energy delivery device 18 is a resistive heating element 46. Itwill be appreciated that the embodiments illustrated in FIGS. 10 and 11are readily adaptable to other thermal energy delivery sources (e.g.,for radiofrequency energy, the resistive heating element is replacedwith insulated RF probe(s) and the energy source is an RF generator).

The temperature of the tissue or of element 46 (FIG. 10) is monitored bysensors 48, and the output power of energy source 20 adjustedaccordingly. The physician can, if desired, override control system 52.A microprocessor can be included and incorporated in the closed or openloop system to switch power on and off, as well as to modulate thepower. The closed loop system utilizes a microprocessor to serve as acontroller 54 which acts to monitor the temperature and adjust the poweraccordingly. Alternatives to the microprocessor are, for example, analogcontrol circuitry and a logic controller.

With the use of sensors 48 and feedback control system 52, a tissueadjacent to resistive heating elements 46 can be maintained at a desiredtemperature for a selected period of time without aberrant hightemperature fluctuations. Each resistive heating element 46 can beconnected to separate control and power supply resources, which generatean independent output for each resistive heating element 46. Forexample, a desired thermal output can be achieved by maintaining aselected energy at resistive heating elements 46 for a selected lengthof time.

When a resistive heating element 46 is used, current delivered throughresistive heating element 46 can be measured by current sensor 56.Voltage can be measured by voltage sensor 58. Resistance and power arethen calculated at power calculation device 60. These values can then bedisplayed at user interface and display 62. Signals representative ofpower and resistance values are received by a controller 54.

A control signal is generated by controller 54 that is related to thecurrent and voltages. The control signal is used by power circuits 66 toadjust the power output in an appropriate amount in order to maintainthe desired power delivered at respective resistive heating elements 46.

In a similar manner, temperatures detected at sensors 48 providefeedback for maintaining a selected power. The actual temperatures aremeasured at temperature measurement device 68, and the temperatures aredisplayed at user interface and display 62. A control signal isgenerated by controller 54 that is related to the actually measuredtemperature and a desired temperature. The control signal is used bypower circuits 66 to adjust the power output in an appropriate amount inorder to maintain the desired temperature delivered at the respectivesensor 48. A multiplexer can be included to measure current, voltage,and temperature at the sensors 48, 56 and 58, so that appropriate energycan be delivered to resistive heating elements 46.

Controller 54 can be a digital or analog controller or a computer withsoftware. When controller 54 is a computer, it can include a CPU coupledthrough a system bus. Included in this system can be a keyboard, a discdrive or other non-volatile memory system, a display, and otherperipherals, as are known in the art. Also coupled to the bus can be aprogram memory and a data memory.

User interface and display 62 includes operator controls and a display.Controller 54 can be coupled to imaging systems well known in the art.

The output of current sensor 56 and voltage sensor 58 is used bycontroller 54 to maintain a selected power level at resistive heatingelements 46. A predetermined profile of power delivered can beincorporated in controller 54, and a preset amount of energy to bedelivered can also be profiled.

Circuitry, software, and feedback to controller 54 result in processcontrol and in the maintenance of the selected power that is independentof changes in voltage or current. Control can include (i) the selectedpower and (ii) the duty cycle (wattage and on-off times). These processvariables are controlled and varied while maintaining the desireddelivery of power independent of changes in voltage or current, based ontemperatures monitored at sensors 48.

In the embodiment shown, current sensor 56 and voltage sensor 58 areconnected to the input of an analog amplifier 70. Analog amplifier 70can be a conventional differential amplifier circuit for use withsensors 48, 56 and 58. The output of analog amplifier 70 is sequentiallyconnected by an analog multiplexer 72 to the input of A/D converter 74.The output of analog amplifier 70 is a voltage which represents therespective sensed parameters. Digitized amplifier output voltages aresupplied by A/D converter 74 to microprocessor 54. Microprocessor 54 maybe a type 68HCII available from Motorola. However, it will beappreciated that any suitable microprocessor or general purpose digitalor analog computer can be used to the parameters of temperature, voltageor current.

Microprocessor 54 sequentially receives and stores digitalrepresentations of temperature. Each digital value received bymicroprocessor 54 corresponds to different parameters.

Calculated power and temperature values can be indicated on userinterface and display 62. Alternatively, or in addition to the numericalindication of power, calculated power values can be compared bymicroprocessor 54 with power limits. When the values exceedpredetermined power or temperature values, a warning can be given onuser interface and display 62, and additionally, the delivery ofelectromagnetic energy can be reduced, modified or interrupted. Acontrol signal from microprocessor 54 can modify the power levelsupplied by energy source 20.

In preferred embodiment of the invention, the materials that make up thevarious parts of an apparatus of the invention have the followingcharacteristics:

    __________________________________________________________________________            Tensile                          Geometry (height,                       Strength in % Conductivity Resisitivity Melt temp. width, and/or dia.)       Component MPa Elongation cal/cm.sup.2 /cm/sec/° C. nΩ*m                                                 ° C. in mm                    __________________________________________________________________________    Mandrel 600-2000                                                                            5-100 N/A      N/A   N/A   height 0.2-2.3                               width 0.05-0.5                                                          Heating Element 300 min. 20 (min.) .025-0.2 500-1500* N/A 0.05-0.5 dia.       Conductor N/A N/A .2-1.0 150 max.* N/A 0.1-0.5 dia.                           Wire                                                                          Plastic sheath N/A 25 (min.) N/A N/A 80° (min.) 0.05-0.2                                                      thickness                            __________________________________________________________________________

Another preferred characteristic is that the minimum ratio heatingelement resistivity to conductor wire resistivity is 6:1; the preferredminimum ratio of guiding mandrel height to guiding mandrel width is 2:1.Tensile strength and % elongation can be measured according to ASTME8(tension test of metallic materials). Conductivity and resistivity canbe determined by procedures to be found in ASTM Vol. 2.03 forelectrothermal properties.

A particularly preferred embodiment of a catheter of the invention canbe prepared using a covering sheath of polyimide with an outsidediameter of 1 mm and a wall thickness of 0.05 mm. Such a sheath providesa significant fraction of the stiffness and torsional strengthappropriate for the catheter. Internal to the polyimide sheath and inthe intradiscal section of the catheter is a heating coil of insulatednickel/chromium wire that has an outside diameter that matches theinterior diameter of the polyimide sheath. This heating coil providesboth heat and additional stiffness to the assembly. Also internal to thepolyimide sheath on each side of the coil (longitudinally) is a 0.1mm-walled, 304 stainless-steel, metallic band whose outer diametermatches the inner diameter of the sheath, the distal band having ahemipsherical end that exits the end of the polyimide sheath and createsa blunt tip 29 at the end of the catheter. These bands provide enhancedratio-opacity for fluoroscopic visualization, as well as some of thestiffness of the assembled apparatus. Proximal to the proximal metallicband and internal to the sheath is an additional polyimide tube 47 thatincreases the stiffness of the catheter in the region that transitionsfrom the intradiscal section containing the coil to the rigid proximalsection. Proximal to the second polyimide tube and internal to thesheath is a 304 stainless steel (fully hard) hypodermic tube with anoutside diameter matching the inside diameter of the polyimide sheathand a wall thickness of 0.1 mm. This combination provides the rigidityneeded for a physician to advance the distal portion of the deviceinside a nucleus polposus and provides tactile force feedback from thetip to the physician.

In some embodiments, inside the bands, coil, hypodermic tube, and boththe polyimide sheath and internal polyimide tube is a guiding mandrelthat extends from a proximal handle to the catheter tip. In oneembodiment, this mandrel is 0.15 mm by 0.5 mm and formed from 304stainless steel. In another embodiment, it is a 0.3 mm diameter 304stainless and steel wire, with the distal 2.5 cm flattened to 0.2 mm by0.5 mm.

Inside the center of the heating coil is a T-type thermocouple pottedwith cyanoacrylate adhesive into a polyimide sheath and locatedalongside the mandrel. The thermocouple wire travels through the coiland hypodermic tube to the handle at the proximal end of the apparatus.Two copper conductor wires (36 gauge insulated with polyimide) aresoldered to the heating coil and pass through he hypodermic tube andhandle to the proximal handle's electrical connector, which allows apower supply and feedback controls to be connected to electricalelements in the catheter. One embodiment has the handle fitted with a1-3 meter cable extension ending in an electrical connector to eliminatethe need for a connector in the handle. This design reduces weight (fromconnector elements) on the proximal end and increases the physician'stactile feedback during device manipulation.

The entire inside of the catheter in one embodiment is encapsulated witha silicone material which removes air (which would insulate the heatcreated by the heating coil) and helps support the polyimide sheath toprevent collapse (i.e., increases stiffness). Instead of the silicone,another embodiment uses an epoxy which remains flexible after curing.Strain relief is provided between the catheter body and the handle withan elastomeric boot. The distal end of the catheter is pre-bent 15-30°of the longitudinal axis of the catheter at about 5-10 mm from thedistal tip.

The catheter in one embodiment carries visible markings 38 on thehypodermic tube (with the markings being visible through the polyimidesheath) to indicate distance of insertion of the catheter into anintroducer and/or distance that the distal end of the catheter extendsout of the introducer into a disc. The catheter is also marked bothvisually and with tactile relief on its handle to indicate the directionof bending of the pre-bent tip and biased stiffness.

The guidable apparatus described herein can be used in any of a numberof methods to treat annular fissures. Specific methods that can becarried out with an apparatus of the invention will now be described.

Discs with fissures can be treated non-destructively with or without theremoval of nucleus tissue other than limited desiccation of the nucleuspulposus which reduces its water content. Fissures can also beameliorated by shrinking the collagen component of the surroundingannulus to bring the sides closer to their normal position. Thermalshrinkage of collagen also facilitates ingrowth of collagen whichincreases annular stiffness. Fissures can also be repaired with sealantssuch as a filler (non-adhesive material that blocks the opening) and/orbonding material (adhesives or cements) which help seal the tear. Thefissure can also be treated with global heating of the disc. Most of theheat will be directed toward the fissure, but the remainder of the discwill also receive some heat.

In some methods of the invention, bonding materials such as collagen,albumin, and a mixture of fibrinogen and thrombin are delivered to thefissure. Collagen from a variety of sources can be used (e.g., bovineextracted collagen from Semex Medical, Frazer Pa., or human recombinantcollagen from Collagen Corp., Palo Alto, Calif.). The collagen isinjected dissolved or as a fine slurry, after which it is graduallythickens (or may be heated) in the fissure, where the injected collagenprovides a matrix for collagen disposition by the body.

A variety of different materials can also be delivered to the fissure,including but not limited to electrolyte solutions (i.e. normal saline),contrast media (e.g., Conray meglumine iothalamate), pharmaceuticalagents (such as the steroid methylprednisolone sodium succinateavailable from Pharmacia & Upjohn, Kalamazoo, Mich., and nonsteroidalanti-inflammatory drugs), chemonucleolytic enzyme (e.g., chymopapain),hydrogel (such as disclosed in U.S. Pat. No. 4,478,822), osteoinductivesubstances (e.g., BMP, see U.S. Pat. No. 5,364,839), chondrocyteinductive substance (e.g., TGG-β) and the like. The materials aredelivered via the catheter and/or introducer to the disc. Preferably,however, when precision placement of the material (as in a fissure) isnecessary or desired, the delivery method uses the apparatus describedabove, especially when delivery to the posterior, posterior lateral, orposterior medial region of the disc is desired. The materials may beadministered simultaneously or sequentially, such as beginning with anelectrolytic solution (which helps the physician view the pathology) andfollowing with products to seal a fissure.

The materials are delivered in an amount sufficient to decrease theextent of the fissure at least partially, preferably to fill the fissurecompletely. The delivered material can be fixed in position with anadhesive, with a hydrogel that is liquid at room temperature but gels atbody temperature, with naturally occurring processes (such asinteraction of fibrinogen and thrombin) within he disc, or by heatingthe disc as described in more detail below.

To seal a fissure, a combination of thrombin and fibrinogen is injectedat the fissure, after which it coagulates and forms a seal over thefissure. A kit with appropriate syringes and other equipment isavailable from Micromedics, Inc., Eagan, Minn. Frozen fibrinogensolution is thawed in its plastic bag and then dispensed to a small medcup. Thrombin is reconstituted with sterile water in the "slow gel"concentration (100 units/ml) for tissue bonding. For example, 100 ml isadded to a vial containing 10,000 units. Thrombin solution is withdrawnfrom the vial and dispensed to a second med cup. The two syringes arefilled equally, one with each solution. Then the syringe tips are eachtwisted into an applicator that mixes the solutions before passing themto an administration tube. The syringes are fitted into the dual syringeholder and the plunger link, which helps the practitioner administerequal amounts of thrombin and fibrinogen. Then the practitioner connectsthe administration tube to the proximal end of the inventive catheter,depresses the plungers and dispenses the sealant solution to thefissure. The thrombin and fibringen react and form a natural seal overthe fissure.

Chymopapain can be injected through the subject catheter, particularlynear a herniation of the disc. Chymopapain splits side chains offproteoglycan molecules, thereby decreasing their ability to hold waterand their volume. The disc gradually loses water and decreases in size.A typical dose is 0.75 to 1.0 ml (2000 pKat/ml).

In some embodiments, thermal energy is delivered to a selected sectionof the disc in an amount that does not create a destructive lesion tothe disc, other than at most a change in the water content of thenucleus pulposus. In one embodiment there is no removal and/orvaporization of disc material positioned adjacent to an energy deliverydevice positioned in a nucleus pulposus. Sufficient thermal energy isdelivered to the disc to change its biochemical and/or biomechanicalproperties without structural degradation of tissue.

Thermal energy is used to cauterize granulation tissue which is painsensitive and forms in a long-standing tear or fissure. Additionally oralternatively, thermal energy is used to seal at least a part of thefissure. To do that, the disc material adjacent to the fissure istypically heated to a temperature in the range of 45-70° C. which issufficient to shrink and weld collagen. In one method, tissue is heatedto a temperature of at least 50° C. for times of approximately one, two,three minutes, or longer, as needed to shrink the tissue back intoplace.

Delivery of thermal energy to the nucleus pulposus removes some waterand permits the nucleus pulposus to shrink. This reduces a "pushing out"effect that may have contributed to the fissure. Reducing the pressurein the disc and repairing the fissure may help stabilize the spine andreduce pain.

Global heating of the disc also can be used to cauterize the granulationtissue and seal the fissure. In this embodiment of the method, theheating element is positioned away from the annulus but energy radiatesto the annulus to raise the temperature of the tissue around thefissure. This global heating method can help seal a large area ormultiple fissures simultaneously.

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

The foregoing description of preferred embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit he invention to the precise formsdisclosed. Many modifications and variations will be apparent topractitioners skilled in this art. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A method of treating an annular fissure in anintervetebral disc comprising:providing a catheter having an intradiscalsection with at least one functional element adjacent a distal end ofthe catheter and a proximal end for externally guiding the distal end ofthe catheter within an intervertebral disc; positioning the functionalelement adjacent the annular fissure by applying a force longitudinallyto the proximal end of the catheter which is sufficient to advance theintradiscal section through the nucleus pulposus and around an innerwall of an annulus fibrosus, but which force is insufficient for theintradiscal section to puncture the annulus fibrosus; and using thefunctional element to treat the annular fissure.
 2. The method of claim1, wherein the step of using the functional element comprises heatingthe disc.
 3. The method of claim 2, wherein the steps of positioning thefunctional element and adding energy are repeated at least once.
 4. Themethod of claim 2, wherein the step of adding sufficient energycomprises adding sufficient energy to cauterize granulation tissue inthe fissure.
 5. The method of claim 2, wherein heating the disc includesdelivering a controlled amount of energy such that no vaporizationoccurs.
 6. The method of claim 2, wherein heating the disc includesdelivering a controlled amount of energy at such that no material otherthan water is removed.
 7. The method of claim 2, wherein the heating thedisc includes delivering a controlled amount of energy such that nodestructive lesion is formed on a disc.
 8. The method of claim 1,wherein providing the catheter is facilitated by a distal end whichdifferentially bends in two orthogonal directions at right angles to thelongitudinal axis.
 9. The method of claim 1, wherein the step ofpositioning the functional element includes positioning the functionalelement in a position selected from the group consisting of at aposterior medial, posterior lateral, anterior lateral, and anteriormedial portion of the annulus fibrosus, and combinations thereof. 10.The method of claim 1, wherein the step of adding sufficient energycomprises adding energy sufficient to shrink the collagen component ofthe annulus fibrosus around the fissure.
 11. The method of claim 1,wherein the step of providing a catheter with at least one functionalelement further includes providing a catheter with a lumen capable ofdelivering or aspirating a material.
 12. The method of claim 11comprising the additional step of placing a material in the disc. 13.The method of claim 12 wherein any of the following are placed:electrolyte solutions, contrast media, pharmaceutical agents,chemonucleolytic enzymes, hydrogel, osteoinductive substances,chdrocyte-inductive substances, sealants, collagen, fibrinogen andthrombin, and any combination thereof.
 14. The method of claim 1 whereinthe step of providing the catheter with at least one functional elementincludes providing a catheter with a heating element and a temperaturesensor.
 15. The method of claim 1, wherein the intradiscal section has abending stiffness as measured in Taber stiffness units between about2-400 units in a desired bending plane.
 16. The method of claim 1,wherein the intradiscal section has a bending stiffness as measured inTaber stiffness units between about 3-150 units in a desired bendingplane.
 17. The method of claim 1, wherein the intradiscal section has abending stiffness as measured in Taber stiffness units between about4-30 units in a desired bending plane.
 18. The method of claim 17,wherein the proximal end of the apparatus has a column strength betweenabout 0.2-7 kg.
 19. The method of claim 17, wherein the proximal end ofthe apparatus has a column strength between about 0.7-4 kg.
 20. Themethod of claim 1, wherein the intradiscal section has a column strengthbetween about 0.05-4 kg.
 21. The method of claim 20, wherein theproximal end of the apparatus has a column strength between about 0.1-25kg.
 22. The method of claim 20, wherein the proximal end of theapparatus has a column strength between about 0.2-7 kg.
 23. The methodof claim 20, wherein the proximal end of the apparatus has a columnstrength between about 0.7-4 kg.
 24. The method of claim 1, wherein theintradiscal section has a column strength between about 0.05-2 kg. 25.The method of claim 24, wherein the proximal end of the apparatus has acolumn strength between about 0.1-25 kg.
 26. The method of claim 24,wherein the proximal end of the apparatus has a column strength betweenabout 0.2-7 kg.
 27. The method of claim 24, wherein the proximal end ofthe apparatus has a column strength between about 0.7-4 kg.
 28. A methodof treating of intervertebral fissure, said method comprisingplacing anenergy source adjacent to the fissure; and providing sufficient energyto the fissure to raise the temperature to at least about 45-70° C. andfor a sufficient time to cause the collagen to weld.
 29. The method ofclaim 28 wherein the step of providing energy is performed to raise thetemperature to at least 50° C. for at least one minute.
 30. The methodof claim 28 wherein the step of providing energy is performed to raisethe temperature to at least 50° C. for at least two minutes.
 31. Themethod of claim 28 wherein the step of providing energy is performed toraise the temperature to at least 50° C. for at least three minutes. 32.The method of claim 28 further comprising the step of placing a sealantin or near the fissure to help seal the fissure.
 33. The method of claim32 further comprising the step of heating the sealant at a temperatureand for a time sufficient to seal the fissure.